This invention relates to electron-emitting devices. More particularly, this invention relates to the structure and fabrication, including repair, of an electron-emitting device suitable for use in a flat-panel display of the cathode-ray tube (xe2x80x9cCRTxe2x80x9d) type.
A flat-panel CRT display basically consists of an electron-emitting device and a light-emitting device that operate at low internal pressure. The electron-emitting device, commonly referred to as a cathode, contains electron-emissive regions that selectively emit electrons over a relatively wide area. The emitted electrons are directed towards light-emissive regions distributed over a corresponding area in the light-emitting device. Upon being struck by the electrons, the light-emissive regions emit light that produces an image on the viewing surface of the display.
The electron-emissive regions are often situated over generally parallel emitter electrodes. In an electron-emitting device of the field-emission type, generally parallel control electrodes cross over, and are electrically insulated from, the emitter electrodes. The electron-emissive regions typically consist of electron-emissive elements exposed through openings in the control electrodes. When a suitable voltage is applied between a control electrode and an emitter electrode, the control electrode extracts electrons from the associated electron-emissive region. An anode in the light-emitting device attracts the electrons to the light-emitting device.
Short circuits sometime occur between the control electrodes, on one hand, and the emitter electrodes, on the other hand. The presence of a short circuit can have a highly detrimental effect on display performance. For example, a short circuit at the crossing between a control electrode and an emitter electrode can prevent the associated electron-emissive region from operating properly.
International Patent Publications WO 98/54741 (Spindt et al) and WO 99/56299 (also Spindt et al) describe field-emission flat-panel CRT displays in which the emitter and control electrodes of the electron-emitting devices are configured in various ways to facilitate repairing control-electrode-to-emitter-electrode short-circuit defects. While the electron-emitting devices of International Patent Publications WO 98/54741 and WO 99/56299 present various advantages, the capacitance at each location where one of the control electrodes crosses over one of the emitter electrodes can cause the devices to have unsuitably low switching speeds. It is desirable to configure the emitter or/and control electrodes in such a way that the control-electrode-to-emitter-electrode cross-over capacitance can be reduced so as to increase the switching speed while still facilitating control-electrode-to-emitter-electrode short-circuit repair.
The present invention furnishes an electron-emitting device, especially one suitable for use in a flat-panel CRT display, in which a specified portion of an electrode, either a control electrode or an emitter electrode, is situated off to the side of the bulk of the electrode. In the case of the control electrode, the specified portion is an exposure portion having openings that expose electron-emissive elements situated over an emitter electrode. In the case of an emitter electrode, the specified portion is an emitter-coupling portion situated below an electron-emissive element exposed through an opening in the control electrode. By having the specified portion of the electrode situated away from the bulk of the electrode, the control-electrode-to-emitter-electrode cross-over capacitance can be made quite small. Should the specified portion of the electrode be electrically short circuited to the other electrode, the specified portion can be readily severed from the remainder of its electrode to remove the short-circuit defect.
More particularly, an electron-emitting device configured in accordance with one aspect of the invention contains an emitter electrode, an electron-emissive region, and a control electrode. The emitter electrode extends longitudinally in a first lateral direction. The electron-emissive region has an electron-emissive zone in which a multiplicity of electron-emissive elements are situated over part of the emitter electrode.
The control electrode consists at least of a rail, an intersection portion, an exposure portion, and a linkage portion. The rail crosses over the emitter electrode and extends longitudinally in a second lateral direction different from the first lateral direction. The intersection portion is continuous with the rail and extends laterally away from it. The exposure portion largely overlies the electron-emissive region and has a multiplicity of openings through which the electron-emissive elements are exposed. The linkage portion extends between, and thereby electrically connects, the intersection and exposure portions.
At least part of the linkage portion of the control electrode is normally situated lateral, i.e., to the side as viewed vertically, of the emitter electrode. The intersection portion of the control electrode is also normally situated lateral to the emitter electrode. As a result, largely only the rail and the exposure portion of the control electrode are situated above the emitter electrode. In as much as the cross-over capacitance between a control electrode and an emitter electrode depends (in part) on the amount of area where the control electrode overlies the emitter electrode, configuring the control electrode in the foregoing way enables the present electron-emitting device to have a very low control-electrode-to-emitter-electrode cross-over capacitance. Accordingly, the switching speed of the electron-emitting device is enhanced, and its power consumption is reduced.
In the course of manufacturing an electron-emitting device configured according to the invention""s teaching, the device can be examined to determine whether the control electrode appears to be short circuited to the emitter electrode at the exposure portion. If so, a cut is made through the linkage portion to electrically separate the exposure portion from the remainder of the control electrode, specifically from the rail and intersection portion. Although the cut causes the exposure portion to become inoperative (disabled), an electron-emitting device having many such exposure portions can often perform adequately when a small number of the exposure portions are inoperative. In such a case, removal of the short-circuited exposure portion repairs the device.
The short-circuit repair operation at the exposure portion of the control electrode is normally done by directing light on the linkage portion of the control electrode. With at least part of the linkage portion being situated lateral to the emitter electrode, the light is typically directed on a part of the exposure portion not vertically in line with the emitter electrode. This enables the short-circuit defect to be removed without significantly affecting the emitter electrode. The configuration of the control electrode thereby facilitates repairing a short-circuit defect between the emitter electrode and the control electrode""s exposure portion.
In one variation of the present electron-emitting device, the control electrode includes a further rail extending longitudinally in the second lateral direction and thus generally parallel to the first-mentioned rail. The intersection portion of the control electrode is continuous with, and extends laterally away from, the further rail so as to be at least partially located between the two rails. The exposure portion is normally situated between the rails.
Use of two rails provides redundancy that enables certain defects involving the rails to be overcome. For instance, if a segment of one of the rails becomes short circuited to the emitter electrode, the short-circuited segment of that rail can be severed from the remainder of the rail and thus from the remainder of the control electrode. Current that would otherwise flow through the short-circuited rail segment is shunted to the other rail and, after passing the short-circuit location, returns (at least partially) to the rail from which the short-circuited segment has been removed. The electron-emitting device can operate in the normal manner even though part of one of the rails is short circuited to the emitter electrode.
In another variation of the present electron-emitting device, the control electrode includes a further linkage portion extending between the exposure portion and a further intersection portion continuous with the rail. Should the first-mentioned linkage portion be defective, the further intersection and linkage portions can provide a current path from the rail to the exposure portion to overcome the defect in the first-mentioned linkage portion. The electron-emitting device of the invention can operate normally even though one of the linkage portions is defective. Should the exposure portion be short circuited to the emitter electrode, cuts can be made through both linkage portions to electrically separate the exposure portion from the remainder of the control electrode.
The electron-emissive region, which is normally one of a group of laterally separated electron-emissive regions each situated opposite a corresponding light-emissive region, may include an additional electron-emissive zone containing a multiplicity of additional electron-emissive elements situated over (another) part of the emitter electrode. In that case, the control electrode includes an additional exposure portion and an additional linkage portion. The additional exposure portion largely overlies the additional electron-emissive zone and has a multiplicity of additional openings through which the additional electron-emissive elements are exposed. The additional linkage portion extends between the intersection portion and the additional exposure portion. By implementing the electron-emissive region with two separate electron-emissive zones, electrons emitted by the electron-emissive region can be better directed toward the oppositely situated light-emissive region.
The lateral configurational features applied to the control electrode for reducing the control-electrode-to-emitter-electrode cross-over capacitance and/or facilitating control-electrode-to-emitter-electrode short-circuit repair are transferred to the emitter electrode in an electron-emitting device configured according to another aspect of the invention. In particular, the emitter electrode in this aspect of the invention consists at least of a rail, an intersection portion, an emitter-coupling portion, and a linkage portion. The emitter-coupling portion replaces the control electrode""s exposure portion in the earlier-mentioned aspect of the invention. The electron-emitting device in this aspect of the invention contains an electron-emissive region having an electron-emissive zone that overlies the emitter-coupling portion. Although typically containing multiple electron-emissive elements in this aspect of the invention, the electron-emissive zone may have as little as one electron-emissive element.
Analogous to the linkage portion of the control electrode in the earlier-mentioned aspect of the invention, the linkage portion of the emitter electrode extends from the intersection portion to the emitter-coupling portion. Subject to the emitter-coupling portion replacing the exposure portion, all of the above-described variations of the control electrode can be applied to the emitter electrode. Configuring the emitter electrode according to this aspect of the invention enables the control-electrode-to-emitter-electrode cross-over capacitance to be reduced and control-electrode-to-emitter-electrode short-circuit repair to be facilitated in the way described above.
In short, an electron-emitting device configured according to the invention has reduced capacitance at locations where a control electrode crosses over an emitter electrode, thereby improving the device""s switching speed and reducing the device""s power consumption. The control or emitter electrode is configured to facilitate repairing short-circuit defects between the emitter and control electrodes. This typically includes shunting current around certain types of short-circuit defects. Defects in the rails and/or linkage portions can be overcome by furnishing the present electron-emitting devices with extra rails and/or extra linkage portions. Accordingly, the invention provides a substantial advance.